Add an error message for calling "GeoJSONSource#setData" for a style that doesn't exist

[gertcuykens]

Can this error message be improved?

(link removed)

Step 1) press the [+] button
Step 2) Notice the specific error message

dispatcher.js:32 Uncaught TypeError: Cannot read property 'send' of undefined

The dispatcher.js:32 that doesn't give any hints whatsoever for me and probably other api users.

[lucaswoj]

The problem stems from calling GeoJSONSource#setData on a source who's style has been removed. We can and should add a better error message in this case.

[stepankuzmin]

I've tried to reproduce this issue with v0.30.0, but it seems that there are no errors at all. Eg. setData on source after removing its style — http://jsbin.com/hohewax/edit?js,console,output

I'm not sure is it is a correct behavior or we should emit an error?

[gertcuykens]

Definitely emit console message please, it's the only failsafe for users like me trying to be a concurrent worker smartass but have no idea they are just making a big race condition mess :) I can't think of any case where the programmer is not making a mistake when manipulating a style that already removed by some other worker?